GP120 immunogens and methods inducing neutralizing antibodies to human immunodeficiency virus

ABSTRACT

The present invention relates, in general, to an HIV-1 vaccine and, in particular, to a B cell lineage-based vaccination protocol.

This application is a U.S. National Phase of International ApplicationNo. PCT/US2012/000442, filed Oct. 3, 2012, which designated the U.S. andclaims priority from U.S. Provisional Application No. 61/542,469, filedOct. 3, 2011 and U.S. Provisional Application No. 61/708,503, filed Oct.1, 2012, the entire contents of each of which are incorporated herein byreference.

TECHNICAL FIELD

The present invention relates, in general, to an HIV-1 vaccine and, inparticular, to a B cell lineage-based vaccination protocol.

BACKGROUND

The traditional strategies for vaccine development have been to makekilled, attenuated or subunit preparations as homologous prime/boosts,and then to test them for safety and efficacy^(1,2). Vaccines developedin this way are used world-wide for both bacterial and viral infectiousdiseases¹⁻⁴. A number of viral targets have so far resisted thisclassical vaccine-development scheme—HIV-1, dengue and hepatitis C amongthem⁵⁻⁷. Broadly protective influenza vaccines have also yet to be beenachieved⁸. HIV-1 is thus a paradigm of those viral diseases for whichinducing broadly neutralizing antibodies is especially difficult^(9,10).

For many of the viral vaccines in current use, induction of neutralizingantibodies is a principal correlate of protection^(3, 4). Efforts tofind new vaccine-development strategies have therefore focused on designof immunogens bearing epitopes with high affinity for plasma antibodiesproduced by memory B cells. This strategy assumes that the antigensrecognized by memory B cells in a vaccine boost are the same as thoserecognized by naïve B cells during the priming immunization. For bothHIV-1 and influenza, however, this strategy has not, as yet, led toinduction in a majority of vaccines of antibodies that neutralize asatisfactorily wide range of virus strains. The failure may stem in partfrom characteristics of the chosen immunogens (e.g., glycan masking ofHIV-1 envelope protein epitopes⁹: Table 1) and in part from limitedaccessibility of conserved epitopes on the viral antigen⁸ (e.g., the“stem” and sialic-acid binding epitopes on influenza HA). Mimicry ofhost antigens by some of these conserved epitopes may be anothercomplication, leading to suppression of a potentially useful antibodyresponse¹¹.

TABLE 1 Factors preventing induction of long-lasting broad neutralizingHIV-1 antibodies Neutralizing epitopes masked by carbohydratesConformational flexibility of HIV-1 envelope Transient neutralizingepitope expression Molecular mimicry of Env carbohydrates and proteinregions of host molecules Tolerance control of gp41 neutralizing epitoperesponses Half-life of all induced antibodies to Env are short; failureof Env to induce long-lived plasma cells Rapid viral escape from inducedneutralizing antibodies Diversion of B cell responses from neutralizingdeterminants by immune dominant, non-neutralizing epitopes of EnvRequirement for extensive somatic hypermutations, and requirement forcomplex maturation pathways

Making vaccines for infectious agents with transient, cryptic orhost-mimicking epitopes may require detailed understanding of antibodyaffinity maturation—in particular, of patterns of maturation that leadto rare, broadly protective antibodies¹²⁻¹⁴. It might then be possibleto design immunogens that increase the likelihood of maturation alongthose pathways. Recent data from animal studies have demonstrated thatthe B cells that survive and persist in the germinal center reaction arethose presenting B-cell receptors with the highest affinity forantigen¹⁵⁻¹⁸. Moreover, for some responses to viral antigens, theantigen that stimulates memory B cells during affinity maturation andthe antigen that initially elicits naïve B cells may not be thesame^(12-14, 19-21). Thus, to induce the processes that lead to such aprotective response, it may be necessary to use one antigen for thevaccine prime (to trigger naïve B cells) and others in boosts that driveaffinity maturation^(12-14, 20-23).

Described herein is an approach to vaccine design based on insights frombasic B cell biology, structural biology, and new methods for inferringunmutated ancestor antibodies as estimates of naïve B-cell receptors andtheir clonal lineage progeny. While the focus is on the biology ofinducing broadly neutralizing antibodies to the HIV-1 Env, parallels arealso drawn to issues for influenza vaccine development.

Biology of B Cells and Antibody Responses.

Human B cells arise from committed progenitors that express the V(D)Jrecombinase, RAG1 and RAG2, to effect genomic rearrangements of the IGHgene loci²⁴⁻²⁷. In pre-B I cells, functional μH polypeptides formed bythese rearrangements associate with surrogate light chains (SLC)²⁸⁻³⁰and Igα/Igβ heterodimers to form pre-B cell receptors (pre-BCR)³¹necessary for cell survival and proliferation^(24, 32, 33). These cellsexit the cell cycle²⁵ as pre-B II cells, initiate rearrangements in theκ- or λ light (L)-chain loci^(34, 35), and assemble a matureBCR^(36, 37) that binds antigen^(24, 38) (FIG. 1). The generation of aBCR by genomic rearrangement and the combinatorial association of IG V,D, and J gene segments ensures a diverse primary repertoire of BCR andantibodies but also produces self-reactive cells with significantfrequency³⁹.

Most immature B cells are autoreactive; they are consequently eliminatedor inactivated by immunological tolerance^(40, 41). The remaining Bcells mature through the transitional 1 (T1) and T2 stages characterizedby changes in membrane IgM (mIgM) density, mIgD expression, and theloss/diminution of CD10 and CD38⁴². In the periphery, newly formed (T2)B cells are subject to a second round of immune tolerization beforeentering the mature B cell pools^(40, 41). Each of these stages inB-cell development is defined by a characteristic genomic andphysiologic status (FIG. 1); in concert, these events specify thepotential of humoral immunity.

At least three mechanisms of immunological tolerance deplete theimmature and maturing B-cell pools of self-reactivity: apoptoticdeletion^(43, 44), cellular inactivation by anergy^(45, 46), and thereplacement of autoreactive BCR by secondary V(D)Jrearrangements^(39, 47-49). The great majority of lymphocytes thatcommit to the B-cell lineage do not reach the immature B cell stagebecause they express dysfunctional μH polypeptides and cannot form apre-BCR^(50, 51) or because they carry self-reactive BCR⁴⁰.

Autoreactive BCR frequencies decline with increasing developmentalmaturity^(43, 47), even for cells drawn from peripheral sites [FIG.1]^(52, 53). The final stages of B-cell development and tolerizationoccur in secondary lymphoid tissues where newly formed (T2) B cellsundergo selection into mature B-cell compartments^(54, 55). Tolerancemechanisms, especially apoptotic deletion⁵⁴⁻⁵⁶, operate during thetransitional stages of B-cell development, and the frequency ofself-reactive cells decreases substantially after entry into the maturepools⁴⁰. The effects of these tolerizing processes have been followeddirectly in humans by recovering and expressing IgH and IgL generearrangements from individual immature, transitional, or mature B cellsand determining the frequencies at which the reconstituted Abs reactwith human cell antigens^(40, 47).

Despite the multiple tolerance pathways and checkpoints, not allautoreactive B cells are removed during development⁴¹. In mice, maturefollicular B cells are substantially purged of autoreactivity, but themarginal zone (MZ) and B1 B cell compartments are enriched forself-reactive cells⁵⁷. In humans, some 20%-25% of mature, naïve B cellscirculating in the blood continue to express autoreactiveBCR^(35, 40, 41).

Not all selection during B-cell development is negative. Carefulaccounting of V_(H) gene segment usage in immature and mature B-cellpopulations suggests that positive selection also occurs in thetransitional stages of B-cell development^(58, 59), but the mechanismsfor such selection are obscure. The substantial selection imposed on theprimary B-cell repertoire, negative and positive, by these physiologicevents implies that the full potential of the primary, or germline, BCRrepertoire is not available to vaccine immunogens. Only those subsets ofnaïve mature B cells that have been vetted by tolerance or remainfollowing endogenous selection can respond. For microbial pathogens andvaccine antigens that mimic self-antigen determinants, the pool ofmature B cells capable of responding can, therefore, be quite small orabsent altogether.

This censoring of the primary BCR repertoire by tolerance sets up a roadblock in the development of effective HIV-1 vaccines as the success ofnaïve B cells in humoral responses is largely determined by BCRaffinity¹⁵⁻¹⁷. If immunological tolerance reduces the BCR affinity andthe numbers of naïve B cells that recognize HIV-1 neutralizing epitopes,humoral responses to those determinants will be suppressed. Indeed,HIV-1 infection and experimental HIV-1 vaccines are very inefficient inselecting B cells that secrete high affinity, broadly neutralizing,HIV-1 antibodies^(5, 60-62).

The predicted effects of immune tolerance on HIV-1 BnAb production hasbeen vividly illustrated in 2F5 VDJ “knock-in” (2F5 VDJ-KI) mice thatcontain the human VDJ gene rearrangement of the 2F5 BnAb^(61, 62). In2F5 VDJ-KI mice, early B-cell development is normal, but the generationof immature B cells is severely impaired in a manner diagnostic oftolerization of auto-reactive BCR^(43, 44). Subsequent studies show thatthe 2F5 mAb avidly binds both mouse and human kynureninase, an enzyme oftryptophan metabolism, at an α-helical motif that matches exactly the2F5 MPER epitope: ELDKWA⁶³ (SEQ ID NO: 1) (Yang, G., Haynes, B. F.,Kelsoe, G. et al., unpublished)

Despite removal of most autoreactive B cells by the central andperipheral tolerance checkpoints^(40, 41), antigen-driven, somatichypermutation in mature, germinal center (GC) B cells generate de novoself-reactivity, and these B cell mutants can become memory Bcells⁶⁴⁻⁶⁶. Thus, Ig hypermutation and selection in GC B cells not onlydrive affinity maturation^(15, 18, 67-69), but also create newlyautoreactive B cells that appear to be controlled onlyweakly^(43, 70-72) by immunoregulation. At least two factors limit thisde novo autoreactivity: the availability of T-cell help^(18, 73) and therestricted capacity of GC B cells to accumulate serial mutations that donot compromise antigen binding and competition for cell activation andsurvival^(18, 67, 74).

Eventually, V(D)J hypermutation approaches a ceiling, at which furthermutation can only lower BCR affinity and decrease cell fitness⁷³⁻⁷⁵. Themean frequency of human Ig mutations in secondary immune responses isroughly 5%^(20, 76, 77), and the significantly higher frequencies(10%-15%) of mutations in Ig rearrangements that encode HIV-1BnAbs^(5, 11) therefore suggest atypical pathways of clonal evolutionand/or selection. In contrast to clonal debilitation by high mutationalburden⁷³⁻⁷⁵, HIV-1 BnAbs appear to require extraordinary frequencies ofV(D)J misincorporation^(5, 11). Perhaps the most plausible explanationfor this unusual characteristic is serial induction of Ig hypermutationand selection by distinct antigens. This explanation also suggestspathways for generating antibody responses that are normally proscribedby the effects of tolerance on the primary BCR repertoire.

In GC, clonally related B cells rapidly divide; their clonal evolutionis a Darwinian process comprising two component sub-processes: Ighypermutation and affinity-dependent selection^(18, 67, 78). Selectionis nonrandom of course, but even hypermutation is non-random, influencedsubstantially by local sequence context⁷⁹ due to the sequencespecificity of activation-induced cytidine deaminase (AICDA)⁸⁰.Furthermore, the codon bias exhibited by Ig genes increases thelikelihood of mutations in the regions that encode the antigen-bindingdomains⁸¹. Even prior to selection, therefore, some evolutionarytrajectories are favored over others. Continued survival andproliferation of GC B cells is strongly correlated with BCR affinity andappears to be determined by each B cell's capacity to collect andpresent antigen^(18, 67) to local CXCR5⁺CD4⁺ T (T_(FH)) cells⁸².

Unlike AICDA-driven hypermutation, where molecular biases remainconstant, clonal selection in GC is relative to antibody fitness(affinity and specificity) and changes during the course affinitymaturation. Individual GC, therefore, represent microcosms of Darwinianselection, and each is essentially an independent “experiment” in clonalevolution that is unique with regard to the founding B and T cellpopulations and the order and distribution of introduced mutations.

The poor efficiency with which either infection or immunization elicitsBnAbs and the unusually high frequency of Ig mutations present in mostBnAb gene rearrangements imply that BnAb B cells are products ofdisfavored and tortuous pathways of clonal evolution. Because BCRaffinity is the critical determinant of GC B cell fitness, it should bepossible to select a series of immunogens that direct GC B-cellevolution along normally disfavored pathways. Any method for directedsomatic evolution must take into account the complex and interrelatedprocesses of Ig hypermutation, affinity-driven selection, and cognateinteraction with T_(FH). These hurdles are not insignificant, butneither are they necessarily insurmountable. Indeed, BnAb responseselicited by HIV-1 infection may represent an example of fortuitoussequential immunizations that, by chance, favor the development of BnAbB cells from unreactive, naïve populations.

Biology of Antibody Responses to HIV-1 as a Paradigm ofDifficult-to-Induce Broadly Neutralizing Antibodies

The initial antibody response to HIV-1 following transmission is tonon-neutralizing epitopes on gp41^(20, 83). This initial Env antibodyresponse has no anti-HIV-1 effect, as indicated by its failure to selectfor virus escape mutants⁸³. The first antibody response that canneutralize the transmitted/founder virus in vitro is to gp120, is ofextremely limited breadth, and appears only ˜12-16 weeks aftertransmission^(84, 85).

Antibodies to HIV-1 envelope that neutralize a broad range of HIV-1isolates have yet to be induced by vaccination and appear in only aminority of subjects with chronic HIV-1 infection⁵ (FIG. 2). Indeed,only ˜20% of chronically infected subjects eventually make high levelsof broadly neutralizing antibodies, and then not until after ˜4 or moreyears of infection⁸⁶. Moreover, when made, broadly neutralizingantibodies are of no clinical benefit, probably because they have noeffect on the well-established, latent pool of infected CD4 T cells⁸⁶.

Goals for an HIV-1 Vaccine

Passive infusion of broadly neutralizing human monoclonal antibodies(mAbs) can protect against subsequent challenge with simian-humanimmunodeficiency viruses (SHIVs) at antibody levels thought to beachievable by immunization⁸⁷⁻⁹⁰. Thus, despite the obstacles, a majorgoal of HIV-1 vaccine development is to find strategies for inducingantibodies with sufficient breadth to be practically useful at multipleglobal sites.

Recent advances in isolating human mAbs using single cell sorting ofplasmablasts/plasma cells^(20,76) or of antigen-specific memory B cellsdecorated with fluorescently labeled antigen protein^(91, 92), andclonal cultures of memory B cells that yield sufficient antibody forhigh throughput functional screening^(22, 93, 94), have led to isolationof mAbs that recognize new targets for HIV-1 vaccine development (FIG.2). Those broadly neutralizing antibodies that are made in the settingof chronic HIV-1 infection have one or more of the following unusualtraits: restricted heavy-chain variable region (V_(H)) usage, longHCDR3s, a high level of somatic mutations, and/or antibodypolyreactivity for self or other non-HIV-1 antigens (rev. in^(5, 11)).Some of these HIV BnAbs have been reverted to their unmutated ancestralstate and found to bind poorly to native HIV-1 Env^(12, 14). Thisobservation has suggested the notion of different or non-nativeimmunogens for priming the Env response followed by other immunogens forboosting^(12-14, 20-23). Thus, the B cell lineage design strategydescribed herein is an effort to drive rare or complex B cell maturationpathways.

SUMMARY OF THE INVENTION

The present invention relates, in general; to an HIV-1 vaccine and, inparticular, to a B cell lineage immunogen design.

Objects and advantages of the present invention will be clear from thedescription that follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. Human B cells arise from committed progenitor cells thatproliferate following expression of functional immunoglobulin heavy-(H-) chain polypeptides that associate with surrogate light chains(SLC). In pre-B I cells. H-chain and SLC pairs associate with Igα/Igβheterodimers to form pre-B cell receptors (pre-BCR) and initiate cellproliferation. When these proliferating cells exit the cell cycle aspre-B II cells, increased RAG1/2 expression drives light- (L-) chainrearrangements and the assembly of mature BCR capable of bindingantigen. Most newly generated immature B cells are autoreactive andconsequently lost or inactivated at the first tolerance checkpoint; theremainder mature as transitional 1 (T1) and T2 B cells characterized bychanges in membrane IgM (mIgM) density, increased mIgD expression, andthe loss/diminution of CD10 and CD38. Newly formed T2 B cells aresubject to a second round to immune tolerization before entering themature B cell pools. Mature B cells activated by antigens and TFHcharacteristically down-regulate mIgD and increase CD38 expression asthey enter the germline center (GC) reaction, GC are sites on intenseB-cell proliferation, AICDA dependent Ig hypermutation and class-switchrecombination, and affinity maturation.

FIG. 2. Schematic diagram of trimeric HIV-1 Env with sites of epitopesfor broadly neutralizing antibodies. The four general specificities forBnAbs so far detected are: the CD4 binding site; the V2,V3 variableloops; certain exposed glycans; and the MPER. Red ovals: gp120 core;dark-red ovals, V1-V2 loops; magenta ovals: V3 loop; blue oval, gp41;bright red stripe: MPER of gp41; light brown, curved stripe: viralmembrane bilayer. The PGT glycan antibodies depend on the N-linkedglycan at position 332 in gp120; like the V2,V3 conformationalantibodies, they also depend on the glycan at position 160.

FIG. 3. Clonal lineage of V2,V3 conformational antibodies, CH01-CH04,their inferred intermediate antibodies (IAs, labeled 1, 2, and 3), andthe inferred unmutated ancestor antibody (UA). Design of immunogens todrive such a pathway might involve producing the UA and IAs and usingstructure-based alterations in the antigen (i.e., changes in gp120 orgp140 predicted to enhance binding to UA or IA) or deriving alteredantigens by a suitably designed selection strategy. Vaccineadministration might prime with the antigen that binds UA most tightly,followed by sequential boosts with antigens optimized for binding toeach IA. For this clonal lineage, an Env known to bind the UA (AE.A244gp120: ref 21) could be a starting point for further immunogen design.

FIG. 4. Monkey study 62.1.

FIG. 5. Monkey study 34.1.

FIG. 6. Levels of binding antibodies to A244 gp120D11 induced byA244gp120D11 alone (NHP #34.1) and sequential Env immunization (NHP#62.1).

FIG. 7. HIV neutralization: comparisons of isolate means (in log₁₀).

FIG. 8. Sequences of A244 gp120 (SEQ ID NO: 2), AE. 427299Δ11gp120 (SEQID NO: 3), and B.9021 gp140C (SEQ ID NO: 4).

FIG. 9. Sequence of 9021 Δ11 gp120 (SEQ ID NO: 5).

DETAILED DESCRIPTION OF THE INVENTION

Definitions of Terms

Autologous neutralizing antibodies: Antibodies that are produced firstafter transmission of HIV-1 and that selectively neutralize thetransmitted/founder virus.

B-cell anergy: A type of B cell tolerance that renders potentiallyresponding B cells unresponsive to antigen.

B-cell tolerance: The activity of the immune system to suppress B cellsthat are dangerously host reactive. These cells are either deleted fromthe B cell repertoire or rendered unresponsive or anergic. A thirdtolerance mechanism is swapping of either light chains (light chainediting) or heavy chains (heavy chain editing) to preventself-reactivity of antibodies.

Broadly neutralizing antibodies (BnAbs): Antibodies produced by B cellsthat neutralize diverse strains of a particular infectious agent.

CD4-binding-site gp120 broadly neutralizing antibodies: The T-lymphocytesurface antigen, CD4, is the cellular receptor of HIV-1. It binds at adefined, conserved site on gp 120. Although many antibodies recognizethe region on the surface gp120 that includes the CD4 binding site,their footprint also covers adjacent parts of the surface, wheremutation can lead to escape from neutralization by those antibodies. Afew, broadly neutralizing antibodies (the VRC01-VRC03 clonal lineage,PG04, the CH30-CH34 clonal lineage) bind gp120 in a way that closelyresembles the contact made by CD4: the heavy-chain VH region of theseantibodies (nearly all are V_(H) 1˜2) mimics the N-terminal, Ig-likedomain of CD4, with relatively few interactions outside the conserved,CD4-binding pocket.

Germinal center: Location in immune tissues at which dendritic and othercells present B cell contact antigen, helper T cells make contact with Bcells, and immunoglobulin class switching and somatic hypermutation takeplace.

Heavy chain third complementary determining region (HCDR3): Three loopsfrom each of the two immunoglobulin polypeptide chains contribute to itsantigen-binding surface. The third of these “complementarity determiningregions” (CDRs) on the heavy chain is particularly variable and oftenmakes a particularly important contribution to antigen recognition.

Hemagglutinin broadly neutralizing determinants: The influenza virushemagglutinin (HA), one of the two principal surface proteins oninfluenza A and B, has, like HIV-1 Env, both strain-specific andconserved determinants for neutralizing antibodies. Like HIV-1 Envneutralizing antibodies, most hemagglutinin neutralizing antibodies arestrain specific and not broadly neutralizing. The conserved targets ofbroadly neutralizing influenza antibodies are the binding pocket for thereceptor, sialic acid, and the “stalk” of the rod-like HA trimer.

Immunoglobulin class switching: The process in germinal centers by whichantigen drives switching of immunoglobulin made by a developing memory Bcell from IgM to IgG, IgA or IgE. This process, which requiresactivation of the recombination activating genes I and II (RAGI, RAGII),is independent of somatic hypermutation. Not all memory B cells undergoclass switching, however, and some memory B cells retain surface IgM.

Intermediate antibodies (IAs): Antibodies made by intermediates in theclonal lineage generated by affinity maturation of a naïve B cell in agerminal center.

Membrane-proximal-external-region (MPER) gp41 broadly neutralizingantibodies: The MPER is a site on HIV-1 Env gp41 near the viral membraneat which a number of neutralizing antibodies bind. Isolated naturalantibodies that bind this region (2F5, 4E10, CAP206-CH12) arepolyreactive; the tip of their HCDR3 associates with the viral lipidmembrane while awaiting exposure of the gp41 intermediate neutralizingdeterminant.

Polyreactivity: the common characteristic of those virus-specificantibodies that also bind either host self antigens or other non-viralantigens.

V2, V3 conformational (quaternary) HIV-1 envelope gp120 broadlyneutralizing antibodies: A group of HIV-1 broadly neutralizingantibodies recognizing an epitope on gp120 that is properly configuredonly (or primarily) when gp120 is part of the complete Env trimer.Mutational analysis of regions of gp120 that bind quaternary antibodiesshow that most of them recognize the second variable (V2) and thirdvariable (V3) loops of HIV-1 Env. Examples include PG9, PG16 and theCH01-04 clonal lineage of human mAbs.

Somatic hypermutation: The process in germinal centers, mediated by theenzyme activation-induced cytidine deaminase (AID), that leads toaffinity maturation of the antibody-antigen contact.

Third variable loop neutralizing antibodies: The third variable loop ofHIV-1 envelope (V3) is part of the binding site for the CCR5 and CXCR4Env co-receptors; it is a frequent target of neutralizing antibodies.Examples of V3 neutralizing antibodies isolated from chronicallyinfected subject are 447, 19b and CH19. The V3 loops is masked on theenvelopes of most transmitted/founder viruses, and thus V3 loopantibodies by themselves are likely to be of limited value as a vaccineresponse. V3 loop antibodies are easily elicited, however, and theycould be useful in combination with an antibody that induced V3 loopexposure (e.g., a CD4-binding-site antibody).

Unmutated ancestor antibodies (UAs): Antibodies that represent the Bcell receptors (BCRs) on naïve B cells. UAs can be isolated from naïveor transitional B cell populations or inferred from memory B-cellmutated clonal lineages.

VH restriction: occurrence of the same V_(H) in the antibody responsesof many different individuals to the same epitope.

B Cell Lineage Vaccine Design

FIG. 3 shows a general outline for B-cell lineage vaccine design. Thereare several points that distinguish this approach from previousvaccination strategies. First, existing vaccines generally use the sameimmunogens for prime as for boosts. In the scheme outlined in FIG. 3,different antigens can be used for multiple steps. Design of the primingantigen can utilize the B cell receptor from the inferred unmutatedancestor (UA, see below) or from an actual, isolated naïve B cell as atemplate, while design of boosting antigens can use the B-cell receptorfrom inferred (or isolated) maturation intermediates as templates (seeimmunogen design section below)⁶⁸. Second, the B cell lineage notiontargets, for the priming immunogen, the earliest stages of B cell clonaldevelopment, following the basic understanding of B cell antigen drivereviewed above (FIG. 1). Third, for boosting immunogens, the scheme inFIG. 3 anticipates choosing components that might have the highestaffinity for early stages of B cell maturation.

Three general steps are contemplated for any lineage-based approach tovaccine design. First, identify a set of clonally related memory Bcells, using single cell technology to obtain the native variable heavy(V_(H)) and variable light (V_(L)) chain pairs. Second, infer with thecomputational methods described below, the unmutated ancestral B-cellreceptor (i.e., the presumptive receptor of the naïve B cell to betargeted), along with likely intermediate antibodies (IAs) at eachclonal lineage branch point (FIG. 2, circular nodes 1-3). Finally,design immunogens with enhanced affinity for UA and IAs, using the UAand IAs as structural templates (FIG. 3). Thus, in contrast to the usualvaccine immunogens that prime and boost with the same immunogen, a Bcell lineage-based vaccination protocol can prime with one immunogen andboost with another, and potentially boost with a sequence of severaldifferent immunogens^(12-14, 20-23) (FIG. 3). In recent work, a gp140Env antigen that did not bind the UA of a BnAb was modified by nativedeglycosylation; unlike the untreated native Env antigen, thedeglycosylated gp140 Env bound the BnAb UA with reasonable efficiency.Immunization of rhesus macaques showed that the Env that bound well tothe UA was the superior immunogen¹⁹.

It is important to note that variability of the antibody repertoireamong individuals poses a potential problem for this strategy: a clonallineage isolated from one subject may not be relevant for inducing asimilar antibody in another subject. Recent observations of limited VHusage summarized above suggest that for some viral neutralizing epitopesthe relevant immunoglobulin repertoire is restricted to a very smallnumber of VH families and that the maturation pathways may be similaramong individuals or require the same immunogens to drive similarpathways of affinity maturation. One example of convergent evolution ofhuman antibodies in different individuals comes from work on B cellchronic lymphocytic leukemia (B cell CLL), in which similar B CLL VHHCDR3 sequences can be found in different people^(95, 96). A secondcomes analysis of influenza and HIV-1 VH1-69 antibodies, in whichsimilar VH1-69 neutralizing antibodies can be isolated from differentsubjects⁹⁷⁻¹⁰¹. A third example comes from structures of V2,V3conformational (quaternary) antibodies in which the antibodies have verysimilar HCDR3 structures but arise from different VHfamilies^(22, 101, 102). Recently, use of 454 deep sequencing technologyhas shown convergent evolution of VH1-2 and VH1-46 CD4 in maturation ofbroadly neutralizing antibodies, but determining how distinct theaffinity maturation pathways are for each specificity of HIV-1 broadlyneutralizing antibodies requires experimental testing. Nonetheless, formajor classes of such antibodies, the data summarized suggestcommonalties among affinity maturation pathways in differentindividuals.

Inferring UAs and Intermediates of BnAb Clonal Lineages

B cell lineage immunogen design requires that it be possible to inferfrom the sequences of the mature mutated antibodies in a lineage thoseof the intermediate and unmutated ancestors, as in the reconstructedclonal lineage in FIG. 2. Antibody genes are assembled from a fixed setof gene segments; that there are relatively small numbers (i.e.,non-astronomical) of possible genes ancestral to any given set ofclonally-related antibody genes allows one to infer the ancestorantibodies²⁰⁻²³.

The starting point for any likelihood-based phylogenetic analysis is amodel for the introduction of changes along the branches. For theinference of unmutated ancestor antibodies of a clonal lineage (See UA,FIG. 3), a model is needed for somatic mutation describing theprobability that a given nucleotide (for example, the one at position 21in the V region gene) that initially has state n₁ will, after thepassage oft units of evolutionary time, have state n₂. This substitutionmodel makes it possible to compute the probability of the observed datagiven any hypothesized ancestor. From there, the application of Bayes'rule provides the posterior probability for any hypothesized ancestor.The posterior probability at each position in the unmutated ancestor cannow be computed from the posteriors over the gene segments and overother parameters of the rearrangement. The complete probability functionprovides a measure of the certainty of the inference at each position inaddition to the most-likely nucleotide state itself. This additionalinformation may be crucial to ensuring the relevance of subsequentassays performed on the synthesized unmutated ancestor. Some of theintermediate forms of the antibody genes through which a given member ofthe clone passed can be similarly inferred, though not all of them(antibodies at nodes 1-3, FIG. 3). The more members of the antibodyclone that it is possible to isolate, the higher the resolution withwhich the clonal intermediates can be reconstructed²⁰. 454 deepsequencing has recently proved useful for expanding the breadth anddepth of clonal lineages^(20, 23).

Using UAs and IAs as Templates for Immunogen Design

The goal of the immunogen-design strategy described herein is to deriveproteins (or peptides) with enhanced affinity for the unmutated commonancestor of a lineage or for one or more of the inferred intermediateantibodies. The method of choice for finding such proteins will clearlydepend on the extent of structural information available. In the mostfavorable circumstances, one might have crystal structures for thecomplex of the mature antibody (Fab) with antigen, structures of the UAand of one or more IAs, and perhaps a structure of an IA:antigencomplex. It is likely that the native antigen will not bind tightlyenough to the UA to enable structure determination for that complex. Inthe absence of any direct structural information, consideration can alsobe given to cases in which the antibody footprint has been mapped by oneor more indirect methods (e.g., mass spectrometry).

Computational methods for ligand design are becoming more robust, andfor certain immunogen-design applications, they are likely to bevaluable¹⁰³. It is anticipated that for the epitopes presented by HIVEnv, however, the available structural information may be too restrictedto allow one to rely primarily on a computational approach. The area ofthe interface between an antibody and a tightly-bound antigen isgenerally between 750 and 1000 Å², and on the surface of gp120, forexample, such an interface might include several loops from differentsegments of the polypeptide chain. Even if both the structure of themature-antibody:Env complex and that of the UA were known, computationaldesign of a modified Env with enhanced affinity for the UA would bechallenging. Selection approaches should, in the near term at least, bemore satisfactory and more reliable.

For continuous epitopes, phage display is a well-developed selectionmethod for finding high-affinity peptides¹⁰⁴. The best-studiedcontinuous epitopes on HIV Env are those for the antibodies, 2F5 and4E10, directed against the membrane proximal external region (MPER) ofgp41. Efforts to obtain neutralizing antibodies by immunization withpeptides bearing the sequence of these epitopes have been generallyunsuccessful, presumably in part because the peptide, even if cyclized,adopts only rarely the conformation required for recognition in thecontext of gp41. In a computational effort to design suitableimmunogens, the 2F5 epitope was grafted onto computationally selectedprotein scaffolds that present the peptide epitope in the conformationseen in its complex with the 2F5 antibody. These immunogens indeedelicited guinea-pig antibodies that recognize the epitope in itspresented conformation¹⁰⁵. The MPER epitopes are exposed only on thefusion intermediate conformation of gp41, however, not on the prefusiontrimer¹⁰⁶, and to have neutralizing activity, these antibodies must havea membrane-targeting segment at the tip of their heavy-chain CDR3 inaddition to a high-affinity site for the peptide epitope¹⁰⁷. Thus, morecomplex immunogens (e.g., coupled to some sort of membrane surface) maybe necessary to elicit antibodies that have both properties.

Differences between antibody 2F5 and its probable unmutated ancestorhave been mapped onto the 2F5 Fab:peptide-epitope complex. The sidechains on the peptide that contact the antibody are all within aten-residue stretch, and several of these (a DKW sequence in particular)must clearly be an anchor segment even for a complex with the UA.Randomization of no more than 5 positions in the peptide would covercontacts with all the residues in the UA that are different from theircounterparts in the mature antibody. Phage display libraries canaccommodate this extent of sequence variation (i.e., about 3×10⁶members), so a direct lineage-based, experimental approach to findingpotential immunogens is possible, by selecting from such librariespeptides that bind the UCA of a lineage or one of the inferredintermediates.

For discontinuous epitopes on gp120 that are antigenic on cell-surfaceexpressed, trimeric Env, a selection scheme for variant Envs can bedevised based on the same kind of single-cell sorting and subsequentsequencing used to derive the antibodies. Cells can be transfected witha library of Env-encoding vectors selectively randomized at a fewpositions, and the tag used for sorting can be, for example, be afluorescently labeled version of the UA antibody. An appropriateprocedure can be used to select only those cells expressing an Envvariant with high affinity for the antibody. In cases for which acomparison has been made of the inferred UA sequence with the structureof an antigen-Fab complex, partial randomization of residue identitiesat 3-5 positions, as in the linear-epitope example, can be expected togenerate the compensatory changes one is seeking.

Recognition of HIV-1 envelope by several classes of broadly neutralizingantibodies includes glycans presented by conformational proteinepitopes. Such antibodies account for ˜25% of the broadly neutralizingactivity in the plasma of subjects selected for broadactivity^(108, 109). By analogy with selection from phage-displayedlibraries, synthetic libraries of glycans or peptide-glycan complexescan be screened to select potential immunogens with high affinity forUAs and IAs of clonal lineages¹¹⁰. Large-scale synthesis of chosenglycoconjugates can then yield the bulk material for immunizationtrials^(111, 112).

The various approaches described herein are equally applicable toinfluenza-virus vaccine design. On the influenza-virus hemagglutinin(HA), two conserved epitopes have received recent attention—one, a patchthat covers the fusion peptide on the “stem” of the elongated HAtrimer^(97, 98, 113), the other, the pocket for binding sialic acid, theinfluenza-virus receptor¹¹⁴. Screens of three phage-displayed librariesof human antibodies, each from a quite different source, yielded similarantibodies directed against the stem epitope, and additional human mAbsof this kind have been identified subsequently by B-cell sorting.Conservation of the stem epitope may be partly a consequence of lowexposure, due to tight packing of HA on the virion surface, and hencelow immunogenicity on intact virus particles. An antibody from avaccinated subject that binds the sialic-acid binding pocket and thatmimics most of the sialic-acid contacts has been characterized¹¹⁴. Itneutralizes a very broad range of H1 seasonal strains.

In summary, HIV-1 is a paradigm for a number of viruses that acquireresistance to immune detection by rapid mutation of exposed epitopes.These viruses do have conserved sites on their envelope proteins but avariety of mechanisms prevent efficient induction by vaccines ofantibodies to these conserved epitopes. Some of these mechanisms, atleast in the case of HIV-1, appear to be properties of tolerance controlin the immune system. It is, therefore, clear that conventionalimmunization strategies will not succeed. Only rarely does the B-cellresponse follow the affinity maturation pathways that give rise to HIV-1or influenza broadly neutralizing antibodies, and until recently therewere no technologies available to define the maturation pathways of aparticular antibody type or specificity. With recombinant antibodytechnology, clonal memory B-cell cultures, and 454 deep sequencing,clonal lineages of broadly neutralizing antibodies can now be detectedand analyzed. Immunogens can be optimized for high affinity binding toantibodies (B-cell receptors of clonal lineage B-cells) at multiplestages of clonal lineage development, by combining analysis of theselineages with structural analysis of the antibodies and their ligands.This combination provides a viable strategy for inducing B-cellmaturation along pathways that would not be taken in response toconventional, single-immunogen vaccines.

Certain aspects of the present invention are described in greater detailin the non-limiting Example that follows.

Example 1

FIG. 4 shows the set of immunizations in NHP study 62.1 whereinimmunogens were chosen based on how well they bound to the antibodymembers of the CH01-CH04 broad neutralizing clonal lineage. A244 gp120delta 11 was used as the prime and the boost was the placebobreakthrough infection in the RV144 trial, 427299.AE gp120 env delta 11,then a further boost with the 9021.B gp140Cenv (but could have beendelta 11 gp120—either one), another boost with A244 gp120 Env delta 11and then another boost with a combination of A244 gp120 delta 11+427299Env. As shown in FIG. 6, when the NHP study 34.1, in which A244 gp120delta 11 alone was used (see FIG. 5)), was compared to NHP study 62.1,in terms of binding of antibodies to A244 gp120 delta 11, similarbinding titers are observed. However, the comparison shown in FIG. 7yields a completely different result. The blue neutralizing antibodylevels are with A244 gp120 D11 Env (study 34.1) and are what was seen inthe plasma of the RV144 trial (Montefiori et al, J. Inf. Dis. 206:431-41(2012)) high titers to the tier 1 AE isolate that was in the vaccineAE92TH023, some other low level tier 1 neutralizing antibody levels, andthe rest of the levels were negative (neutralizing antibody assay levelsin this assay start at a plasma dilution of 1:20 such that levels on thegraph of “10” are below the level of detection and are read asnegative). In contrast, the titers to the tier 1s in the red bars fromstudy 62.1 show 1-2 logs higher abs to the tier 1s but most importantlynow significant neutralizing antibody levels to the two tier 2transmitted founder breakthrough viruses from the RV144 trial (allassays in TZMBL assay, except for the two arrows indicate HIV isolateswhich were assayed in the A3R5 cell neutralizing antibody assay). Thus,by immunizing with sequential Envs chosen for their ability to optimallybind at UCA, IA and mature antibody member points of a broadneutralizing antibody lineage, the breadth of neutralizing antibodycoverage has been increased by inducing new neutralizing antibodies toTier 2 (difficult to neutralize) HIV strains AE.427299 and AE.703357,demonstrating proof of concept that the strategy of B cell lineageimmunogen design can indeed induce improved neutralizing antibodybreadth. Moreover, these data demonstrate a new discovery as a strategyfor inducing greater breadth of neutralization in using theALVAC/AIDSVAX type of vaccine (Haynes et al, NEJM 366: 1275-1286 (2012))for future vaccine trials, and that is adding gp120 Envs to the primerand or the boost regimen made up of Env gp120s chosen from thebreakthrough infections that did not match the original vaccine in RV144to increase the potency of vaccine efficacy of a vaccine in Thailand.Rolland has shown that if the RV144 trial breakthrough viruses arecompared from vaccinees and placebo recipients, those viruses that hadsimilarity at the V2 region were controlled by 45% vaccine efficacy(Rolland M et al, Nature September 10, Epub ahead of print, doi:10.1038/nature 11519, 2012). Thus, screening the sequences of RV144breakthrough viruses for the most common HIV strains with Env V2 regionsthat did not match the vaccine should demonstrate the Env V2 motifs thatshould be included in additional prime or boosting Envs in the nextvaccine to increase the vaccine efficacy. In addition, the adjuvant usedwill be important. In the trials above in NHP study 34.1 and 62.1 theadjuvant used was a squalene based adjuvant with TLR7+TLR9 agonistsadded to the squalene (see PCT/US2011/062055). Currently availableadjuvants that are available and can be considered for use in humans isMF-59 (Dell'Era et al, Vaccine 30: 936-40 (2012)) or AS01B (Leroux-Roelset al, Vaccine 28: 7016-24 (2010)). Thus, a vaccine can be designedbased on a polyvalent immunogen comprising a mixture of Envsadministered in sequence as shown, for example, in FIG. 4 oralternatively the sequentially chosen Envs can be administered alltogether for each immunization as describe (Haynes et al, AIDS Res.Human Retrovirol. 11:211-21 (1995)) to overcome any type ofprimer-induce suppression of Env responses. Thus, the present inventionrelates, at least in part, to an approach to improving the RV144 vaccineby adding gp120s or gp140Cs (with or without the delta 11 (D11)deletion) (e.g., 427299 Env gp120 sequences) to the A244 gp120 immunogento expand the coverage of the RV144 original vaccine. (See, for exampleFIGS. 4 and 5.) It can be seen that this strategy of probing thebreakthrough viruses of any partially successful vaccine trial canutilize this strategy to improve that vaccines coverage of infectiousagent strains and in doing so, improve the vaccine efficacy of thatvaccine.

The present invention also relates in part to demonstrating proof ofconcept of the general strategy of vaccine design known as “B CellLineage Immunogen Design” wherein the prime and boost immunogens arechosen based on the strength of binding of each vaccine component to anantibody template in the antibody clonal lineage that is desired toinduce.

All documents and other information sources cited herein are herebyincorporated in their entirety by reference. Also incorporated byreference is U.S. Provisional Application No. 61/542,469, filed Oct. 3,2011 and International Application No. PCT/US2011/000352, filed Feb. 25,2011.

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What is claimed is:
 1. A method of inducing an immune response in amammal comprising sequentially administering to said mammal a primeimmunogen and a boost immunogen, wherein the prime immunogen comprisesall the consecutive amino acids after signal peptide sequenceMRVKETQMNWPNLWKWGTLILGLVIICSA in SEQ ID NO: 2 and wherein the boostimmunogen comprises all the consecutive amino acids after signal peptidesequence MRVKGIRKNCQQHLWRWGTMLLGILMICSA in SEQ ID NO:
 4. 2. A method ofinducing an immune response in a mammal comprising sequentiallyadministering to said mammal a prime immunogen and a boost immunogen,wherein the prime immunogen comprises all the consecutive amino acidsafter signal peptide sequence MRVKETQMNWPNLWKWGTLILGLVIICSA in SEQ IDNO: 2 and wherein the boost immunogen comprises all the consecutiveamino acids after signal peptide sequence MRVKETQRSWPNLWKWGTLILGLVIMCNAin SEQ ID NO:
 3. 3. The method of claim 1, further comprisingadministering at least one further boost immunogen.
 4. The method ofclaim 3, wherein the further boost immunogen is selected from the groupconsisting of a boost immunogen comprising all the consecutive aminoacids after signal peptide sequence MRVKETQMNWPNLWKWGTLILGLVIICSA in SEQID NO: 2, a boost immunogen comprising all the consecutive amino acidsafter signal peptide sequence MRVKETQRSWPNLWKWGTLILGLVIMCNA in SEQ IDNO: 3, and a boost immunogen comprising all the consecutive amino acidsafter signal peptide sequence MRVKGIRKNCQQHLWRWGTMLLGILMICSA in SEQ IDNO:
 5. 5. The method of claim 2, further comprising administering atleast one further boost immunogen.
 6. The method of claim 5, wherein thefurther boost immunogen is selected from the group consisting of a boostimmunogen comprising all the consecutive amino acids after signalpeptide sequence MRYKETQMNWPNLWKWGTLILGLVIICSA in SEQ 2, a boostimmunogen comprising all the consecutive amino acids after signalpeptide sequence MRYKGIRKNCOOHLWRWGTMLLGILMICSA in SEQ ID NO: 4, and aboost immunogen comprising all the consecutive amino acids after signalpeptide sequence MRVKGIRKNCOOHLWRWGTMLLGILMICSA in SEQ ID NO:
 5. 7. Themethod of claim 6, further comprising administering all the consecutiveamino acids after signal peptide sequence MRVKETQMNWPNLWKWGTLILGLVIICSAin SEQ ID NO: 2 and all the consecutive amino acids after signal peptidesequence MRVKETQRSWPNLWKWGTLILGLVIMCNA in SEQ ID NO: 3 as an additionalfurther boost.
 8. A composition comprising an immunogen comprising allthe consecutive amino acids after signal peptide sequenceMRVKETQMNWPNLWKWGTLILGLVIICSA in SEQ ID NO: 2 and an immunogencomprising all the consecutive amino acids after signal peptide sequenceMRVKETQRSWPNLWKWGTLILGLVIMCNA in SEQ ID NO:
 3. 9. The composition ofclaim 8, further comprising, an adjuvant.
 10. The method of claim 4,further comprising administering all the consecutive amino acids aftersignal peptide sequence MRVKETQMNWPNLWKWGTLILGLVIICSA in SEQ ID NO: 2and all the consecutive amino acids after signal peptide sequenceMRVKETQRSWPNLWKWGTLILGLVIMCNA in SEQ ID NO: 3 as an additional furtherboost.
 11. A method of inducing an immune response in a mammalcomprising sequentially administering to said mammal a prime immunogenand a boost immunogen, wherein the prime immunogen comprises all theconsecutive amino acids after signal peptide sequenceMRVKETQMNWPNLWKWGTLILGLVIICSA in SEQ ID NO: 2 and wherein the boostimmunogen comprises all the consecutive amino acids after signal peptidesequence MRVKGIRKNCQQHLWRWGTMLLGILMICSA in SEQ ID NO:
 5. 12. The methodof claim 11, further comprising administering at least one further boostimmunogen.
 13. The method of claim 12, wherein the further boostimmunogens are selected from the group consisting of a boost immunogencomprising all the consecutive amino acids after signal peptide sequenceMRVKETQMNWPNLWKWGTLILGLVIICSA in SEQ ID NO: 2, a boost immunogencomprising all the consecutive amino acids after signal peptide sequenceMRVKETQRSWPNLWKWGTLILGLVIMCNA in SEQ ID NO: 3, and a boost immunogencomprising all the consecutive amino acids after signal peptide sequenceMRVKGIRKNCQQHLWRWGTMLLGILMICSA in SEQ ID NO:
 4. 14. The method of claim13, further comprising administering all the consecutive amino acidsafter signal peptide sequence MRVKETQMNWPNLWKWGTLILGLVIICSA in SEQ IDNO: 2 and all the consecutive amino acids after signal peptide sequenceMRVKETQRSWPNLWKWGTLILGLVIMCNA in SEQ ID NO: 3 as an additional furtherboost.
 15. The method of any of claims 1, 2-7, 10-14 further comprisingadministering an adjuvant.
 16. The method of claim 15, wherein theadjuvant is a squalene-based adjuvant.
 17. The method of claim 15,wherein the adjuvant further comprises TLR7 and TLR9 agonists.